PM levels on an underground metro platform: A study of the train, passenger flow, urban background, ventilation, and night maintenance effects

The negative effect of airborne particles on human beings has been widely noticed in recent decades. The high particle mass concentrations on underground platforms can be a significant public health issue for underground metro systems. This study monitored PM10, PM2.5, and PM1 particle mass concentrations in a field measurement performed from January to December 2020 on an underground metro platform in Stockholm, Sweden. A linear mixed model, named the multi-factor model, was set up based on the measurement results. The model contains the commuting effects, which are train frequency, train type and passenger flow, and the non-commuting effects, which are urban-background air quality, ventilation, night maintenance, and the accumulation effect in an hourly step. The R2 values of the multi-factor model when estimating platform hourly PM10, PM2.5, and PM1 levels are 0.89, 0.88 and 0.86. All factors in the model are statistically significant. According to the model, the train frequency, train type, passenger flow, urban background air quality, and night maintenance positively correlate with the platform PM concentrations. The train frequency effect is more significant for PM10 particles than the train type effect, and the train type effect is more evident for PM1 particles. The passenger flow effect contributes more to the PM1 levels than other coarser particles. The ventilation system can notably decrease the platform PM concentrations for all particle sizes.QC 20220112